Exemplary embodiments pertain to the art of strain gauges and, in particular, to a strain gauge for a tube that can be used, for example to drive actuators in an aircraft.
Modem aircraft often use a variety of high lift leading and trailing edge devices to improve high angle of attack performance during various phases of flight, for example, takeoff and landing. One such device is a trailing edge flap. Current trailing edge flaps generally have a stowed position in which the flap forms a portion of a trailing edge of a wing, and one or more deployed positions in which the flap extends forward and down to increase the camber and/or plan form area of the wing. The stowed position is generally associated with low drag at low angles of attack and can be suitable for cruise and other low angle of attack operations. The extended position(s) is/are generally associated with improved air flow characteristics over the aircraft's wing at higher angles of attack.
In general, such devices can include a control unit that causes a main drive unit to produce rotation of a shaft or “torque tube”. This rotation can then be converted to flap extension in known manners such as by use of a ball screw. In such systems, each flap typically includes two actuators, one for each side of the flap.
The speed and position of the torque tubes are measured but not the amount of axial/torsional force that is applied to drive the aircraft surfaces. The actuation system will react to over/under speeds and to surfaces being out of position, but not to an over torque scenario.
In some cases the control surface can get stuck or other problems may occur. Such problems will result in an increase/decrease of torque in the shaft. Being able to measure such changes could be useful in certain instances.